Schistosomiasis, a debilitating disease caused by Schistosoma mansoni, is estimated to affect 200-300 million people world-wide. At present, reduction in transmission of the infecting parasite and chemotherapy using praziquantel are the main approaches available to control the disease. Clinical and experimental evidence, showing that natural immunity does exist in the infected host, give encouraging indications that it should be possible to develop an effective vaccine against schistosomiasis. Furthermore, extensive on-going work being carried out to understand the immune response modulation during infection or following vaccination using attenuated parasites in mice and rat models indicate that CD4+ T- lymphocytes play a major role in protective immunity. Foreign protein molecules are taken up by antigen-presenting cells such as macrophages and B-lymphocytes and are processed within these cells by unfolding and proteolysis to short peptide fragments. These fragments are then displayed on the cell surface, bound to MHC class II molecules. Binding of T-cell receptor to these peptides in the context of MHC molecules triggers a cascade of T-helper (Th) cell immune responses. Elegant methodological developments have made it possible to elute these peptides from purified MHC molecules by acid extraction and to analyze them by microsequencing. The goal of this proposal is to isolate and identify important T-cell epitopes of schistosome origin using this novel methodological approach. The Specific Aims of this proposal are: 1) Isolation and identification of MHC class II bound S.mansoni peptides. Eluted peptides will be sequenced nd large quantities of appropriate peptides will be synthesized for further studies. 2) To elicit immune response in mice sing "immuno- dominant" synthetic peptides. Synthetic peptides, constructed on the basis of positive proliferation response and Th1-type cytokine secretions in the T-cell screening assay and sequence homology with S. mansoni antigen, will be used to address this aim of the proposal. 3) To generate and characterize T-cell lines and clones against immuno-dominant peptides. This will be achieved by establishing T-cell lines and clones from lymph node cells of mice immunized with synthetic peptides. These T-cell clones will be characterized for antigen specificity, cytokine secretion profile, and capacity to generate in vitro and in vivo anti-parasite responses; and 4) To study in vivo protective response in Balb/c, C57BL/6, SJL and CBA/J mice following immunization with synthetic peptides. We have presented data showing that peptides eluted from MHC class II molecules extracted from A20 cell line pulsed with AP40 extract of schistosomule stimulate a proliferative response in bulk lymph node cells harvested from vaccinated BALB/c as well as C57BL/6 mice. Data has also been presented to establish that the techniques related to generating and maintaining antigen-specific cell lines and hybridomas are in routine use in our laboratory, as are the assays needed for their characterization. We are therefore confident that the project we have submitted is a feasible one and that it can be completed successfully.